Re: K75 Temp Light Always On

[Laitch]

The diagnostic test published by forum member rbm indicates fan failure at pin E when pin E is grounded indicates a faulty temperature switch (relay). If rbm indicates something is amiss, I tend to believe it.

The flickering warning light raises questions about the temperature switch's ability to accurately monitor the coolant/engine temperature and provide accurate data to the FICU also. If the temperature switch or its wiring to other components is faulty, bypassing the switch to run the fan ignores the possibility of other function problems in that system, including sending incorrect data to the FICU because there' a problem in the coolant temperature sensor's circuit, too?

I seem to have lost the plot here.   I'm probably distracted by needing to put my Brick into my winter storage shed tomorrow.

[Steveboot]

It would be helpful to see the internal diagram for the fan relay, but I haven't come across that yet.

The tests I've seen done are from the socket side with the relay removed. But if the relay is removed no amount of jumpers on the socket will get it to pick up. So, tests that jumper the relay contact from the socket side are effective. And tests that put a ground on the socket to complete the lamp circuit are effective. But a test that grounds the pin of the socket that bypasses the temperature sensor would do nothing.

I need to apply voltage to the relay unit to see if its contact picks up to start the fan. But that test would have to be done with the relay in the socket. Or just applying voltage to the relay outside of the socket.

The (+) terminal of the relay appears to be A3, but for that to work the impedance of the coil and the lamp would have to be such that the relay picks up before the lamp lights. I've seen similar in older control circuits but its a bit of crap and small changes in impedance can result in a dim light when there shouldn't be any.

I'm guessing the diagram is drawn in a misleading way. It also is not clear what the (-) terminal is. If I had to guess, pin E is on the (-) side and feeds the relay through a diode, and all the outputs are isolated from each other through diodes. That could mean I have a bad diode or a bad relay.

Anyone have the actual internal wiring diagram?

[Laitch]

Here's a link to an excellent schematic.

Pin E is connected to one of the terminals of the coolant temperature sensor. Opening the switch box carefully to view the works may be your only option to get a detailed understanding beyond what the schematic provides concerning the interior layout of the temperature switch.

A defect in the coolant temperature sensor or its wiring circuit could be involved, too. That could involve the FICU. The flickering warning light seems problematic. Sometimes, new parts are defective, too, sad to say.